The present invention relates to an apparatus such that two video appliances such as a television camera and a controlling unit thereof (will be referred to a "CCU", i.e., Camera Control Unit) are coupled with each other by employing a single transmission path through which a video signal, an audio signal, and a control signal are multiplexed and transmitted in a bidirectional manner.
Conventionally, in case that for example, a television camera (will be abbreviated as a "camera" hereinafter) is coupled with a CCU, and the video, audio, and control signals are multiplexed and transmitted between them in the bidirectional manner, such a conventional method is well utilized in that the triple coaxial cable called as "TRIAX" is frequency-divisionally multiplexed. In this conventional method, as represented in FIG. 2, three sorts of video (picture) signals R, G, B obtained from the camera 1 and four sorts of audio signals A1, A2, A3, A4 obtained therefrom are transmitted from the camera 1 to the CCU 2. On the other hand, the video signal M for a monitor (not shown), the audio signal A5 for instructing a cameraman (not shown either), and the control signal D for controlling the operation of the camera 1 are transmitted from the CCU 2 to the camera 1.
Also, to bidirectionally transmit a plurality of signals to a single cable 7, these signals occupy the different frequency bands (ranges), as represented in FIG. 3, by amplitude-modulating the carrier waves with the different frequencies. As a result, all components can be separated in the camera 1 and the CCU 2 without any interference from the signals present on the cable 7 at the same time by way of the filter provided on either the camera 1 or the CCU 2.
In FIG. 4, there is shown a schematic structural diagram of the conventional analog transmission system. In this drawing, a signal transmitting/receiving apparatus 143 is connected to a camera 131. Another signal transmitting/receiving apparatus 144 is connected to a CCU 138. These transmitting/receiving apparatuses 143 and 144 are coupled with each other by a transmission cable 135. Reference numerals 139, 140, 141, 142 show gate circuits capable of separating a transmission signal from a reception signal. The video signal, the audio signal, and the control signal, which are obtained from the camera 131, are processed in a frequency division/multiplex processing circuit 132 of transmitting/receiving apparatus 132 in such a manner that carrier waves having different frequencies are amplitude-modulated (AM) to produce signals having different frequency bands (ranges), and then these AM signals are multiplexed. Then, the multiplexed signal is transmitted via a cable 135 to the CCU 138 side. On the CCU side 138, the multiplexed AM signal transmitted from the camera 131 side is separated by a filter employed in a separating circuit 137 in such a way that all of the signal components contained in this multiplexed signal are separated without any mutual interference.
Similarly, the video signal, the audio signal, and the control signal, which are derived from the CCU 138 side, are processed in another frequency division/multiplex processing circuit 136 in such a manner that these signals are modulated to obtain the modulated signals having different frequency bands from those of the AM signals used in the camera side 131, and then these modulated signals are multiplexed. Then, the multiplexed signal is transmitted to the camera 131 side. On the camera side 131, the multiplexed signal transmitted from the CCU 138 side is separated by way of a filter of another separating circuit 133.
As described above, a plurality of signals are transmitted via a single cable 135 in the bidirectional manner. Here, in the television camera system, these apparatuses must be synchronized with each other. For instance, when a plurality of camera systems (a single camera system is constructed by a set of a camera and a CCU) are operated at the same time, video signals produced from a plurality of cameras must be synchronized with each other.
In such a television studio system that a selection is made of any one of plural camera systems and an image outputted from the selected camera system is externally sent out, the frame phases of the image signals derived from a plurality of camera systems must be mutually made coincident in order that when the plural camera systems are switched, the images are not interrupted, or not brought into synchronous states. This treatment implies the camera synchronization.
Conventionally, such a synchronizing operation is known in the art that one sync (synchronization) signal is commonly supplied to all of the CCUs, and the synchronizing operations are carried out in the respective CCUs on the basis of this single sync signal. Similarly, the respective cameras are synchronized with the respective CCUs based on this single sync signal. With employment of such a system, a plurality of camera systems can be synchronized with each other.
Referring now to FIG. 4, the synchronizing operations between the camera 131 and the CCU 138 will be described.
To synchronize the video phase of the camera 131 with the video phase (for instance, frame phase) constituting the operation bases for the respective apparatuses employed in the CCU side 138, conventionally, the video phase signal (for example, frame signal) 9 of the CCU 138 is modulated and multiplexed in a similar manner to the video signal, and then the resultant signal is transmitted to the camera 131. On the camera 131 side, the video phase signal is separated from the multiplexed signal transmitted from the CCU 138 by way of the filter of the separating circuit 133. Then, a reference video phase signal is produced in a reference video phase signal generating circuit 134, so that the camera 131 is operable on the basis of this reference video phase signal. As a result, the video phase of the camera 131 may be synchronized with the video phase of the CCU 138.
With employment of the above-described synchronizing methods, both of the synchronizing process in the video phases between the camera and the CCU, and also the bidirectional signal transmission could be achieved in the conventional transmission systems. However, all of these signal synchronizing processes are carried out in the analog form. That is, since the signals are amplitude-modulated to be transmitted in the above-described multiplex transmission apparatus, the video signal and the audio signal produced from the camera side, or the CCU side are adversely influenced by the cable characteristic or the filter characteristic, resulting in deterioration of the signal characteristics. As a consequence, the conventional multiplex transmission systems owns such a problem that there is a limitation in the signal transmittable distance.
On the other hand, the transceiver with the bidirectional simultaneous transmitting/receiving system is disclosed in PCT patent application No. WO91-02414 opened in 1991 in the radio communication field.